Magnesite is a carbonate mineral (MgOCO ₃ ) of crystalline or latent crystal structure, and its theoretical content of MgO is 47.82%. It is widely used in refractory industry, such as magnesium powder metallurgical quality basic refractory products; state of caustic magnesite was also used in industrial electrolysis Magnesium and carbon calorimetry and construction industry.

China's natural magnesite resources are extremely rich, ranking first in the world. In particular, the magnesite ore reserves in southern Liaoning are large and concentrated, and the quality is good. It is an important base for the production of alkaline refractory raw materials in China's metallurgical industry. The manganese ore mine of Liaoning Magnesium Mine has proven reserves of 800 million tons. Among them, the low grade tertiary mine accounts for about 20% of the mine's reserves. For a long time, the mine mainly mines primary mines and some secondary mines. Low-grade tertiary mines have not been included in the mining plan due to quality problems. This situation will undoubtedly cause great waste of magnesite resources in the region. Therefore, it is a strategic issue to be solved urgently to find a rational use of such ore and give full play to the resource advantages of the region.

This paper only discusses the beneficiation and purification of our low-grade three-grade magnesite in Huazi, and discusses some of the main influencing factors in the process of sorting.

I. Overview of ore properties

Hua Yu three sub-magnesite ore composition is relatively simple, mainly for magnesite and talc, chlorite (chlorite leaves, oblique chlorite), dolomite and pyrite and so on. A small amount of chlorite is present in the magnesite and dolomite in the form of a similar substance. The crystal of the magnesite also contains a certain amount of dolomite fine machine maple inclusions. Magnesite and gangue mineral dolomite are uniformly and unevenly embedded in coarse and medium-sized granules respectively; talc, chlorite and iron are uniformly embedded in medium-fine granules and fine granules. The mosaic between the continuous minerals is closely related, and the residual bodies are irregularly adjacent to each other. The multi-element analysis of the ore minerals was: IL 47.94%, SO ₂ 4.00%, AL ₂ O ₃ 0.97%, Fe ₂ O ₃ 0.48%, CaO 0.93%, and MgO 46.05%.

Second, the test and results

According to the ore nature of the low-grade tertiary magnesite of Huazizi and its requirements for use, a section of grinding was adopted in the selection of the plan, -200 mesh accounted for 70%, the second-stage anti-floating silicate gangue mineral and a section The open sorting process of flotation magnesite. In the selection of magnesite, the related new agents were explored. The selection process is shown in Figure 1, and the results are shown in Table 1.

Figure 1 Low-grade three-stage magnesite sorting process

Table 1 Test results of low grade tertiary magnesite

It can be seen from the test results that the selection conditions are reasonable, and the three-stage magnesite adopts the process flow to obtain two products of high-purity magnesium concentrate and secondary concentrate. Among them, the high purity concentrate clinker MgO content can be selected as 98.58%, and the total impurity content of SiO ₂ +CaO+Fe ₂ O ₃ +Al ₂ O ₃ is 1.42%. The expected quality indicators were fully met.

Third, the main factors affecting the sorting

(1) Grinding fineness

In order to examine the effect of grinding fineness on the sorting process, a two-stage reverse floating silicate mineral process was used for the test. The test results show that when the content of -200 mesh is increased from 60% to 90%, the SiO ₂ content in the concentrate decreases with the increase of grinding fineness within a certain range; when the fineness reaches 70%-200 mesh, The SiO ₂ content remains unchanged; in all concentrates of the fineness range, the MgO content is substantially at the same level. The yield is significantly reduced as the fineness increases. Accordingly, according to the monomer dissociation inspection result of the grinding product, when the grinding fineness is 70%-200 mesh, the monomer solution height of the magnesite has reached more than 95%. Therefore, it is appropriate to control the grinding degree to -200 mesh to 70%.

(2) Deamination of dodecylamine at natural pH

From the study of the dissociation state of dodecylamine, it is known that the dissociation of dodecylamine in solution depends on the pH of the medium. When the concentration of dodecylamine is 1×10 ^-4 mol, RNH ₃ ⁺ , RNH ₃ (water-soluble) and RNH ₂ (insoluble) corresponding to different pH values ​​are calculated; in the acidic medium, RNH ₃ ^{+ is} dominant; Between 7 and 10, RNH ₃ ⁺ gradually decreases; when pH=10.65, the same amount of RNH ₃ ⁺ and RNH ₂ (water-soluble) are present in the solution; when pH>10, the insoluble RNH is precipitated from the solution. ₃ At this time, RNH ₃ ^{+ is} drastically reduced. The test results can also be confirmed. When the dosage of dodecylamine is 200g/t, the pH value is increased from 0 to 7, and the yield of gangue minerals increases. After the pH exceeds 7, the yield of gangue minerals decreases rapidly. Its optimal anti-floating pH is between 6 and 7. Therefore, it is obviously appropriate to use the natural pH value in the reverse float stage.

Figure 2 shows the effect of dodecamine on the anti-floating process at the natural pH. It can be seen from the figure that as the amount of dodecylamine increases, the content of SiO _{2 in the} concentrate decreases, and the rate of decrease is significantly increased. When the amount of dodecylamine exceeds 250 g/t, the concentration of amine ions in the slurry is increased. Increasing, its adsorption on the surface of the gangue mineral gradually shifts from electrostatic adsorption to "half micelle adsorption", the electric potential sign changes, and the adsorption and desorption equilibrium. Results The SiO ₂ content in the concentrate and the reduction rate of SiO _{2 in the} concentrate gradually reached the same level. At this point, it is no longer practical to continue increasing the amount of amine. Therefore, under the premise of ensuring the quality of high-purity magnesium concentrate, it is undoubtedly beneficial to select the amount of dodecylamine in the anti-floating range of 250-300 g/t.

Figure 2 Effect of dodecamine content on sorting index at natural pH

Curve 1 - Concentration of concentrate SiO ₂ Curve _{2 -} Content of SiO _{2 in} concentrate

(III) Adjustment of pH value during the process of Zhengfu magnesite

Studies have shown that the zeta potential of the magnesite is positive in the range of pH 3.8 to 11.0, and its zeta potential is fluctuating between 11.9 and 53.7 mV (Fig. 3 curve 1). Since magnesite is a soluble mineral, most of the Mg ^{2 +} ions can be transferred from the surface to the solution; a very small amount of CO ₃ ^{2 -} ions forms H ₂ CO ₃ with the H ⁺ ions in the solution after increasing the pH of the solution. A portion of the H ⁺ ions are adsorbed on the surface of the magnesite as opposite charged ions in the electric double layer. When the pH of the solution is increased, the solubility of the lattice ions on the surface of the magnesite decreases, and the zeta potential value decreases. The electrokinetic potential of the magnesite is still positive in the alkaline range, under which the MgOH ⁺ compound is formed on the mineral surface. The number of adsorbed active sites changed significantly. Curve 2 in Fig. 3 is the result of examining the effect of pH on the floatability of magnesite by using oxidized paraffin soap (400 g/t) as a collector . It has been found that the flotation effect between pH 6 and 8 is extremely poor, which may be related to the adsorption of the collector in the polymerization layer. When the pH is between 8.5 and 11.0, the flotation effect is the best. Therefore, it can be confirmed that the adjustment of the pH value is of great significance to the entire positive magnesite process.

Figure 3: Motorized potential and floatability of magnesite

Curve 1 - the electrokinetic potential of magnesite

The relationship between curve 2 and pH and the floatability of magnesite

(4) Water glass dosage

Water glass is a commonly used gangue mineral inhibitor. Its inhibition increases as the colloidal silicic acid component {(SiO ₂ )m·yH ₂ SiO ₃ ·xSiO ₃ ^{2 -} } 2xH ⁺ increases. In this research, the amount of water glass is 750~1250g/t. From the test results, when the dosage is increased to 1000g/t, the content of SiO ₂ in the high-purity concentrate can be reduced to 0.04%, and the reduction rate of SiO ₂ can be It reached 99.43%. Obviously, this indicator is satisfactory.

Studies have shown that the hydrolysis-composite balance of water glass in aqueous solution is as follows:

In medium and alkaline pulps, water glass is mainly adsorbed on the surface of minerals in the form of [SiO(OH) ₃ ^- ] and [SiO ₂ (OH) ₃ ^{2 -} ]. Although the mineral surface is sometimes negatively charged, these components can still adsorb on the surface and enhance the surface electronegativity. This characteristic of water glass determines its important position in the magnesite sorting process. Experimental study also concluded that during the flotation magnesite, sodium hexametaphosphate and sodium silicate phosphor mixture, can bring the water glass inhibition.

(5) Collector oxidized paraffin soap

A large number of studies from magnesite flotation have shown that unsaturated and saturated fatty acids and their soaps can be used as their collectors.

Fatty acids and their soaps are weak electrolytes that dissociate into RCOOH in water. ROOO ^- +H ⁺ , whose dissociation constant decreases as the hydrocarbon chain lengthens. The length of the hydrocarbon chain has an impact on its capture performance. Studies have also shown that within a certain range, the increase in the number of carbon atoms in the hydrocarbon chain will increase its ability to capture. However, if the hydrocarbon chain is too long, the solubility of the chemical agent will decrease, which will result in poor dispersion in the slurry and lower the collection performance. The hydrocarbon chain O ₁₅ -O _{40 of} oxidized paraffin soap, which is the main component of the flocculation process, is a carboxylic acid. Therefore, it exhibits high chemical activity, low freezing point and strong absorption capacity and selectivity. Etc.

In the experimental study, the pH of the slurry was adjusted to 9 and flotation was carried out at a temperature of 22 °C. According to the test results, when the oxidized paraffin soap is changed between 320 and 560 g/t, the grade of the obtained high-purity concentrate MgO is basically maintained at the same level, which is more than 47% (clinker MgO>98%). . Increasing the amount of oxidized paraffin soap only affects the yield of high purity magnesium concentrate. The above advantages and characteristics of oxidized paraffin soap are shown. Therefore, it is feasible to use oxidized paraffin soap as a collector in the process of positive float magnesite.

(6) Low temperature flotation collector

As is known, oxidized paraffin soap as a collector has the disadvantage of being highly sensitive to the temperature of the slurry and not effective at low temperature flotation. In general, the temperature requirement of the pulp is controlled at about 25 °C, which makes it difficult to use oxidized paraffin soap in the northeast region where the average annual temperature is low, and it will increase energy consumption. Therefore, it is necessary to find a new type of collector that is conducive to low temperature flotation: to reduce energy consumption and mineral processing costs.

After preliminary studies on several new agents, it was found that W collectors have better low temperature flotation performance. The test results conducted at a dosage of 550 g/t and a slurry temperature of 13 ° C showed that the W collector was very similar to the oxidized paraffin soap in the same process. The flotation results of the W collector was 550 g/t and the flotation temperature was 13 ° C. Table 2 shows the results.

Table 2 W harvesting test (13 ° C) flotation test results

The above-mentioned exploration test of W collectors has undoubtedly laid a good foundation for the development of new flotation of magnesite flotation. There is also a special in-depth study in the future.

Fourth, the conclusion

(1) The composition of the low-grade magnesite minerals of Huazizi is relatively simple. The difference in physical properties between magnesite and main gangue minerals is conducive to obtaining high purity products. The research determines the process of the production of a coarse-sweeping anti-floating silicate mineral and a positive-floating magnesite. The process is simple, the ore dressing cost is low, and the index of formation is good. Among them, the high-purity magnesium concentrate has a MgO content of 47.48% (clinker MgO>98%) and a secondary concentrate MgO content of 44.35% (clinker MgO>88%). The high-purity magnesium concentrate in the two products can be used to produce high-purity magnesia, and secondary concentrates can also be used. This has found a new way for the rational development and utilization of low-grade magnesite in the region.

(2) In the process of reverse flotation, the use of dodecylamine at natural pH can effectively exclude silicate-like gangue minerals. Adjusting the pH to the alkaline range (8.5 to 11.0), the addition of water glass can selectively change the loading state of the surface of the magnesite and gangue minerals, which is a prerequisite for the good floatability of the magnesite, and then the oxidation is used. When paraffin soap is used as a collector, it is an ideal high-purity product.

(3) Exploratory tests on new W collectors are expected to achieve better results in low-temperature flotation in further research.

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